The present invention relates to flower-like polymer nano-particles, methods for their preparation, and their use as, for example, additives for rubber, including natural and synthetic elastomers. The invention advantageously provides several mechanisms for surface modifications and general characteristic tailoring to improve performance in rubbers, elastomers, and thermoplastics.
Polymer nano-particles have attracted increased attention over the past several years in a variety of fields including catalysis, combinatorial chemistry, protein supports, magnets, and photonic crystals. Similarly, vinyl aromatic (e.g. polystyrene) microparticles have been prepared for uses as a reference standard in the calibration of various instruments, in medical research and in medical diagnostic tests. Such polystyrene microparticles have been prepared by anionic dispersion polymerization and emulsion polymerization.
Nano-particles can be discrete particles uniformly dispersed throughout a host composition. Nano-particles preferably are monodisperse in size and uniform in shape. However, controlling the size of nano-particles during polymerization and/or the surface characteristics of such nano-particles can be difficult. Traditional spherical nano-particles may have a high number of chain ends in the individual nano-particles. It has been theorized that these chain ends may alter the hysteresis values of rubber compositions modified with nano-particles. Accordingly, achieving better control over the surface composition, i.e., decreasing the number of polymer chain ends in the nano-particle surface layers, of such polymer nano-particles also is desirable.
Rubbers may be advantageously modified by the addition of various polymer compositions. The physical properties of rubber moldability and tenacity are often improved through such modifications. Of course, however, the simple indiscriminate addition of nano-particles to rubber is likely to cause degradation of the matrix material, i.e., the rubber, characteristics. Moreover, it is expected that primarily the selection of nano-particles having suitable size, material composition, and surface chemistry, etc., will improve the matrix characteristics.
In this regard, development of nano-particles having a surface layer with fewer chain ends, which would be compatible with a wide variety of matrix materials, is desirable because discrete particles could likely disperse evenly throughout the host to provide a uniform matrix composition. However, the development of a process capable of reliably producing acceptable nano-particles has been a challenging endeavor. For example, the solubility of various monomers in traditional alkane solvents has made solution polymerization a difficult process by which to achieve nano-particles having a variety of surface layers. Moreover, the development of a solution polymerization process producing reliable nano-particles, particularly nano-particles advantageously employed in rubber compositions, has been elusive.